Removable pressure sensitive adhesives with plasticizer resistance properties

ABSTRACT

A removable, plasticizer resistant pressure sensitive composition that is particularly useful for PSA applications on plasticizer containing vinyl films is provided. The pressure sensitive adhesive comprises: (a) at least one hydrophobic monomer, (b) about 0.2 to about 10 wt. % of at least one hydrophilic monomer; (c) about 1 to about 40 wt. % of one partially hydrophilic monomer (d) an effective amount of a crosslinker selected from diallyl maleate or a compound represented by the formula (I): (I), wherein R is selected from hydrogen, methyl, or ethyl, and R′ is selected from vinyl, allyl, or methallyl; wherein the pressure sensitive adhesive does not contain a plasticizer.

BACKGROUND OF THE INVENTION

This invention relates to removable pressure sensitive adhesives basedon aqueous emulsions. The removable pressure sensitive adhesives of thisinvention have enhanced plasticizer resistance properties which areparticularly useful for pressure sensitive adhesive applications onplasticizer containing vinyl films.

Removable pressure sensitive adhesives are used on a variety of productsincluding labels, tapes, films, and the like, to enable the product toadhere to a substrate and then later to be removed from the substratewithout difficulty and without leaving a stain or residue. To besuitable for such applications, the pressure sensitive adhesive musthave good adhesion with low initial peel strength and must not exhibit asignificant increase in adhesion over time. Optimally, the pressuresensitive adhesive should exhibit such physical properties on a varietyof substrates. Typical commercially available aqueous emulsion removablepressure sensitive adhesives have anchorage and removability weaknesswhen used with plasticizer containing facestocks such as vinyl films.

Plasticizers usually are moderately high molecular weight organicliquids, or occasionally low melting solids, which are incorporated in amaterial to increase its workability, flexibility, or distensibility.For example, polyvinyl chloride (PVC) or, as it is more commonlyreferred to, “vinyl”, in its unmodified form, is typically rigid. Whencompounded with a plasticizer, it becomes more flexible and can be usedfor broader applications. Plasticized vinyl typically contains 15-50% byweight of either a monomeric or polymeric plasticizer, with themonomeric plasticizers being more commonly employed. The monomericplasticizers are of relatively low molecular weight and tend to migrateto the surface of the plasticized vinyl. When a typical pressuresensitive adhesive is applied to a plasticized vinyl film and allowed toremain in contact with it for an extended period of time, plasticizerfrom the vinyl tends to migrate into the pressure sensitive adhesive,softening it and causing a decrease in adhesion. Pressure sensitiveadhesives that have high initial peel strength are more resistant toplasticizer, however, the resulting decreased removability isundesirable.

Attempts have been made to solve the plasticizer migration problem byinterposing an impenetrable barrier between the vinyl and the pressuresensitive adhesive (“PSA”); see, e.g., U.S. Pat. Nos. 4,045,600 and4,605,592. Others have developed pressure sensitive adhesives that aresaid to be less susceptible to weakening by plasticizer, see U.S. Pat.No. 4,985,488. Another attempt to prevent migration of plasticizer froma plasticized vinyl substrate into a confronting pressure sensitiveadhesive has been to incorporate plasticizer into the pressure sensitiveadhesive, thereby minimizing the plasticizer gradient between thecontacting layers; see, e.g., published European Pat. App. No. EP150,978 A, and PCT publication no. WO 00/36043.

Despite the limited success achieved by products of the type discussedabove, there has remained a strong commercial desire for pressuresensitive adhesives that not only maintain strong anchorage to a varietyof vinyl films, but also maintain good removability.

SUMMARY OF THE INVENTION

According to this invention, a removable, plasticizer resistant pressuresensitive adhesive (PSA) is provided comprising a crosslinked aqueousemulsion polymer comprising: (a) at least one hydrophobic monomerselected from an alkyl (meth)acrylate ester of an alcohol wherein thealkyl portion of the alcohol is linear or branched and contains at least4 carbon atoms; (b) about 0.2 to about 10 wt. % of at least onehydrophilic monomer; (c) about 1 to about 40 wt. % of one partiallyhydrophilic monomer selected from alkyl (meth)acrylate esters of analcohol wherein the alkyl portion of the alcohol has 1 to 2 carbonatoms, N-vinyl-2-pyrrolidone, or mixtures thereof; and (d) an effectiveamount of crosslinker selected from diallyl maleate or compoundsrepresented by the formula:

wherein R is selected from hydrogen, methyl, or ethyl, and R′ isselected from vinyl (—HC═CH₂), allyl (—CH₂—CH═CH₂), or methallyl(—C(—CH₂)═CH₂); wherein the pressure sensitive adhesive does not containa plasticizer.

As used herein, a PSA is “removable” and “plasticizer resistant” if,when the PSA is applied to a vinyl film facestock, the PSA has aninitial peel value upon removal from a substrate of less than about 0.3pounds per inch with the failure mode being essentially adhesivefailure, and maintains a peel value (after aging for 7 days at 70° C.)of less than about 0.3 pounds per inch with essentially no transfer ofadhesive to the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

Not Applicable.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides aqueous emulsion PSA polymers that possess goodplasticizer resistance properties and are removable. The product of thisinvention is particularly useful when used with plasticizer containingfilms such as window graphics applications, where low stable peel,non-ghosting and clean removability from glass and stainless steel arerequired. The pressure sensitive adhesives of the invention maintainstrong anchorage to a variety of vinyl films, including films ofpolymers and co-polymers of vinyl chloride, and exhibit good plasticizerresistance and removability from the substrate.

The extent of removability can be determined by measuring the force (inpounds) needed to remove an adhesive/facestock film construction from aspecific test surface using a 180° C. peel angle with a constant peelrate under conditions of constant temperature and humidity. PSAs withclean removability have low initial peel values of less than about 0.3pound per inch with failure mode being essentially adhesive failure.

The removable, plasticizer resistant pressure sensitive adhesivecompositions of this invention comprise a crosslinked aqueous emulsionpolymer comprising: (a) at least one hydrophobic monomer selected froman alkyl (meth)acrylate ester of an alcohol wherein the alkyl portion ofthe alcohol is linear or branched and contains at least 4 carbon atoms;(b) about 0.2 to about 10 wt. % of at least one hydrophilic monomer; (c)about 1 to about 40 wt. % of one partially hydrophilic monomer selectedfrom alkyl (meth)acrylate esters of an alcohol wherein the alkyl portionof the alcohol has 1 to 2 carbon atoms, N-vinyl-2-pyrrolidone, ormixtures thereof; and (d) an effective amount of a crosslinker selectedfrom diallyl maleate or compounds represented by the formula:

wherein R is selected from hydrogen, methyl, or ethyl, and R′ isselected from vinyl (—HC═CH₂), allyl (—CH₂—CH═CH₂), or methallyl(—C(—CH₂)═CH₂); provided that the pressure sensitive adhesive does notcontain a plasticizer. As used herein, the phrase “pressure sensitiveadhesive does not contain a plasticizer” means that the PSA, both aspolymerized and as formulated for application to a vinyl film facestock,does not contain a plasticizer. Once applied to a vinyl facestock, thePSAs of the invention will allow the migration of a finite amount ofplasticizer from the vinyl film into the PSA.

The hydrophobic monomer that can be employed according to this inventioninclude at least one alkyl (meth)acrylate ester of an alcohol whereinthe alkyl portion of the alcohol is linear or branched and contains atleast 4 carbon atoms. As used herein, the term alkyl (meth)acrylateincludes both alkyl acrylates and alkyl methacrylates. The alkyl groupsof the alkyl acrylate or alkyl methacrylate monomers are preferablylinear or branched alkyl radicals having from 4 to about 14 carbonatoms, more preferably from 4 to about 10 carbon atoms, and mostpreferably from 4 to about 8 carbon atoms. Examples of suitable alkylacrylates and alkyl methacrylates include isooctyl acrylate,4-methyl-2-pentyl acrylate, 2-methyl-butyl acrylate, isoamyl acrylate,sec-butyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, isodecylmethacrylate, isononyl acrylate, isodecyl acrylate, and the like, singlyor in mixtures of two or more. The currently preferred alkyl acrylate oralkyl methacrylate ester monomers are 2-ethylhexyl acrylate, n-butylacrylate, and mixtures thereof.

The amount of hydrophobic monomers, based on the total weight ofmonomers (a), (b), (c) and (d), is from about 50 to about 90 wt. %,preferably about 60 to about 84 wt. %, and more preferably from about 70to 80 wt. %.

Hydrophilic monomers that can be employed according to this inventionare monomers that are copolymerizable with the hydrophobic monomer andthat are water soluble. The hydrophilic monomers are selected frommonoolefinic monocarboxylic acids, monoolefinic dicarboxylic acids,2-hydroxyethyl acrylate, or mixtures thereof.

Examples of suitable hydrophilic monomers include, but are not limitedto, acrylic acid, methacrylic acid, fumaric acid, maleic acid, itaconicacid, crotonic acid, oligomeric acrylic acid, 2-hydroxyethyl acrylate,and mixtures thereof. The currently preferred hydrophilic monomers areacrylic acid, 2-hydroxyethyl acrylate, methacrylic acid, and mixturesthereof.

The amount of hydrophilic monomers, based on the total weight ofmonomers (a), (b), (c) and (d), is from about 0.2 to about 10 wt. %,preferably about 0.2 to 5 wt. %, and more preferably about 1 to 3 wt. %.

Partially hydrophilic monomers that can be employed according to theinvention include alkyl (meth)acrylate esters of an alcohol wherein thealkyl portion of the alcohol has 1 to 2 carbon atoms,N-vinyl-2-pyrrolidone, or mixtures thereof. The partially hydrophilicmonomers can also be referred to as partially water soluble monomers.

Examples of suitable partially hydrophilic monomers include methylacrylate, methyl methacrylate, ethyl acrylate, N-vinyl-2-pyrrolidone,and mixtures thereof. The currently preferred partially hydrophilicmonomers are ethyl acrylate, ethyl methacrylate, and mixtures thereof,with ethyl acrylate being currently most preferred.

The amount of partially hydrophilic monomers, based on the total weightof monomers (a), (b), (c) and (d), is from about 1 to about 40 wt. %,preferably from about 10 to about 25 wt. %, and more preferably fromabout 12 to about 25 wt. %.

An effective amount of the crosslinkers of the invention is used for thepreparation of the removable, plasticizer resistant PSAs of theinvention. In addition to the composition of monomers (a), (b) and (c)of the invention, the addition of an effective amount of the crosslinkerof the invention is another critical feature of the invention. Theaqueous emulsion polymer of the invention is sufficiently crosslinkedsuch that the resulting crosslinked PSA network is sufficiently loose toallow enough plasticizer penetration to prevent plasticizer build-up atthe PSA-vinyl film interface, and yet tight enough to limit the mobilityof the aqueous emulsion polymer chains and prevent peel strengthbuild-up. Consequently, the pressure sensitive adhesives of the instantinvention achieve both good anchorage and clean removability from thesubstrates to which the PSAS are applied.

The crosslinkers that can be employed by this invention include diallylmaleate, and compounds represented by the formula:

wherein R is selected from hydrogen, methyl or ethyl, and R′ is selectedfrom vinyl (—HC═CH₂), allyl (—CH₂—CH═CH₂), or methallyl (—C(—CH₂)═CH₂).

Examples of suitable crosslinkers include allyl acrylate, allylmethacrylate, vinyl acrylate, vinyl methacrylate, methallyl acrylate,methallyl methacrylate or mixtures thereof.

The amount of the crosslinker, based on the total weight of monomers(a), (b), (c) and (d), is about 0.2 wt. % to about 1.0 wt. %, andpreferably from about 0.3 to 0.6 wt. %.

The aqueous PSA compositions of this invention, both as polymerized andas formulated, do not contain plasticizers. Plasticizers tend to destroyadhesion to vinyl film and cause transfer failure, or migrate onto thesubstrate to which PSAs are applied and leave a residue of plasticizeron the substrate when the PSA is removed. It is also preferred not toinclude waxes in the PSA compositions of the invention.

The process for the preparation of the removable, plasticizer resistantpressure sensitive adhesives of the invention utilizes at least onewater-soluble polymerization initiator. Any conventional water-solublepolymerization initiator that is normally acceptable for emulsionpolymerization of acrylate monomers may be used and such polymerizationinitiators are well known in the art. The typical concentration ofwater-soluble polymerization initiators is about 0.01 wt. % to about 1wt. %, preferably about 0.01 wt. % to about 0.5 wt. %, of the totalweight of monomers (a), (b), (c), and (d) charged in the pre-emulsion.The water soluble polymerization initiators can be used alone or used incombination with one or more conventional reducing agents, such asbisulfites, metabisulfites, ascorbic acid, sodium formaldehydesulfoxylate, ferrous sulfate, ferrous ammonium sulfate, ferricethylenediamine-tetraacetic acid, and the like. Water-solublepolymerization initiators that can be employed according to theinvention include water soluble persulfates, peroxides, azo compoundsand the like, and mixtures thereof. Examples of water soluble initiatorsinclude, but are not limited to, persulfates (e.g. potassium persulfate,and sodium persulfate), peroxides (e.g. hydrogen peroxide, andtert-butyl hydroperoxide), and azo compounds (e.g.4,4′-azobis(4-cyano-pentanoic acid), V-501 from Wako Chemicals).Currently the preferred water soluble polymerization initiators are thepersulfates, particularly potassium persulfate.

The polymerization can be initiated by any conventional method known tothose skilled in the art, such as by application of heat or radiation.The method of initiation will be dependent on the water-solublepolymerization initiator used and will be readily apparent to thoseskilled in the art.

The water soluble polymerization initiator can be added to thepolymerization reaction in any conventional manner known in the art. Itis currently preferred to add the initiator to the initialpolymerization reactor charge which comprises water. Alternatively, aninitial amount of the polymerization initiator can be added to theinitial reactor charge and the remainder of the initiator addedcontinuously or incrementally during the emulsion polymerization.

At least one surfactant is utilized in the polymerization and it iscurrently preferred to add the surfactant with water and the monomers tofrom a pre-emulsion. The pre-emulsion is then charged to thepolymerization reactor and the polymerization conducted.

The surfactants that can be employed include anionic, nonionic,cationic, or amphoteric emulsifiers and mixtures thereof. Ionicemulsifiers are currently preferred, with anionic emulsifiers beingcurrently most preferred. Examples of suitable anionic emulsifiersinclude, but are not limited to, alkyl aryl sulfonates (e.g. sodiumdodecylbenzene sulfonate), alkyl sulfates (e.g. sodium dodecyl sulfate,ammonium dodecyl sulfate), sulfates of ethoxylated alcohols (e.g. sodiumlauryl ether sulfate), sulfates and sulfonates of ethoxylatedalkylphenols (e.g. ammonium nonylphenol ether (EO=30) sulfate, sodiumsalt of alkylaryl polyether sulfonates), sulfosuccinates (e.g. sodiumdioctyl sulfosuccinate), diphenyl sulfonates (e.g. sodium dodecyldiphenyloxide disulfonate), and mixtures thereof. Examples of suitablenonionic emulsifiers include, but are not limited to, ethoxylatedalcohols (e.g. ethoxylated oleyl alcohol), ethoxylated alkylphenols(e.g. nonylphenol ethoxylate), and mixtures thereof. Examples ofsuitable cationic emulsifiers include, but are not limited to,ethoxylated fatty amines (e.g. ethoxylated tallow amine).

The typical concentration of surfactant is based on the total weight ofmonomers (a), (b), (c) and (d), and is about 0.1 to about 5 wt. %,preferably about 0.5 to about 3 wt. %.

The polymerization reaction can be conducted in any conventionalreaction vessel capable of an emulsion polymerization. It can beconducted at a temperature typical for emulsion polymerizations,preferably at a temperature in the range of about 50° C. to about 95°C., most preferably in the range of about 55° C. to about 85° C.

The polymerization time is that time needed to achieve the desiredconversion based on the other reaction conditions, e.g. temperatureprofile, and reaction components, e.g. monomers, initiator, etc. Thepolymerization time will be readily apparent to those skilled in theart.

Following polymerization, if the pH of the latex emulsion is not withinthe desired pH range of about 6 to about 9, and more preferably about 6to about 8, the pH of the emulsion is adjusted by contacting the latexemulsion with a suitable base in an amount necessary to raise the pH tothe desired pH. Examples of suitable bases for adjusting the pH of thelatex emulsion include alkali metal hydroxides, alkaline earth metalhydroxides, ammonium hydroxide, amines, and the like, and mixturesthereof.

The latex emulsion typically has a solids content of from about 40 toabout 70 wt. %, and preferably about 55 to about 65 wt. %.

EXAMPLES

-   Material: Abbreviation/Material Information-   Ethyl Acrylate EA; CAS [140-88-5] Dow, Celanese, BASF-   Butyl Acrylate BA; CAS [141-32-2] Dow, Celanese, BASF-   Acrylic Acid (glacial) AA; CAS [79-10-7] Celanese, BASF-   Allyl Methacrylate ALMA; CAS [96-05-9] AGEFLEX AMA, Mhoromer-   Potassium Persulfate PPS; CAS [7727-21-1] FMC Corp-   Sodium Bicarbonate NaHCO₃; CAS [144-55-8] Church & Dwight-   Aerosol NPES 30/30 Ammonium salt of    poly(oxy-1,2-ethanediyl)-α-sulfo-ω(nonylphenoxy); CAS[9051-5-4]    Cytec-   Aerosol OT (75% active) Sodium dioctylsulfosuccinate; CAS    [2673-22-5] Cytec-   Triton X-305 (70% active) Octyl phenoxypolyethoxyethanol; CAS    [9036-19-5] Dow-   Trigonox AW-70 CAS [75-91-2] Akzo Nobel-   Parolite Zinc formaldehyde sulfoxylate; CAS [24887-06-7] Cognis Corp-   NoFoam 1976 Defoamer; mixture of surfactants; Oil Chem Technologies-   Kathon LX Biocide CAS [26172-554], [2682-20-4] Rohm & Haas-   Diallyl Maleate DAM; CAS [999-21-3] ALDRICH    Peel Testing Procedure:

PSA 180° C. Angle Dynamic Peel test was conducted to determine the force(in pounds) needed to remove an adhesive/carrier film construction froma specific test surface using a 180° C. peel angle with a constant peelrate under conditions of constant temperature and humidity. Wet adhesivewas coated on release liner at certain coat weight. The wet adhesive wasair dried for 15 min before being placed in an oven (90° C.) for 5 min.drying. The adhesive was then transferred to a vinyl film facestock. Asample test strip of 1″×5″ was applied to a substrate, and 1 lb pressurewas applied. The test strip(s) were subjected to the specified testconditions of time, temperature and humidity. [Note: Tests were at leastrun in duplicate.] Peel strength was determined in an Instron TestMachine (Model No. 1125) by peeling a strip from the substrate at an180° C. angle.

In reporting results, the mode of the peel failure is identified asfollows: “a” meaning adhesive failure, i.e. adhesive entirely separatesfrom the substrate, “c” meaning cohesive failure, i.e. the adhesive isleft partially on the substrate and partially on the facestock, “t”meaning transfer failure, i.e. the adhesive is all transferred to thesubstrate, and “g” meaning some type of material being deposited on thesurface of the test substrate but can not be classified as polymeric innature and does not exhibit any significant degree of tack. A peelfailure mode of “a” is acceptable. A peel failure mode of “c” or “t” isunacceptable as adhesive is left on the substrate. Abbreviations forpeel testing conditions are identified as follows: PL(24 hr): Peelstrength at 24 hours; PL(1 wCh: Peel strength after 1 week underconstant temperature and humidity; PL(3d 70° C.): Peel strength after 3days at 70° C.; PL(1 w 70° C.): Peel strength after 1 week at 70° C.;PL(1 w Hum): Peel strength after 1 week under constant humidity; PL(20min): Peel strength at 20 min.; PL(20 hr): Peel strength at 20 hours;PL(4d@65° C.): Peel strength after 4 days at 65° C.; and PL(4d 70° C.):Peel strength after 4 days at 70° C.

Example 1

Materials are charged as the following. Pilot plant and lab have thesame recipe, only different scale. All data, charge, and scales weretaken from lab conditions.]

The following table is lab scale charge. Reactor Preemulsion PreemulsionFirst Second Material Charge Surfactant Charge Monomer Charge Post-addPost-add Total Water 262.2 141.1 5.05 408.4 Sodium 2.00 2.00 BicarbonatePotassium 3.36 3.36 Persulfate Aerosol NPSE 16.13 16.13 30/30 TritonX-305 1.5 1.5 (70%) Aerosol OT 5.84 5.84 (75%) Acrylic Acid 12.09 12.09Ethyl Acrylate 97.05 97.05 ALMA 3.31 3.31 Butyl Acrylate 448.3 448.3Trigonox A- 0.50 0.50 W70 (70%) Parolite 0.41 0.41 Nofoam 1976 1.16 1.16Kathon LX 0.12 0.12 Total 267.6 164.6 560.7 7.12 0.12 1000Polymerization Procedure:

Water and initiator PPS were charged in the polymerization kettle (2liter reactor) and agitation began. Aerosol NPSE, Triton X-305, andAerosol OT were premixed in a pail with water and the mixture was thenadded to a delay tank. The mixture was agitated in the delay tank tillthe surfactants are uniformly miscible with water. Under agitation, thepreemulsion monomers were charged to the delay tank in the followingorder of addition: acrylic acid, ethyl acrylate, allyl methacrylate,butyl acrylate. Monomers and surfactants were mixed together at thedelay tank to form a white milky preemulsion. The reactor contents wereheated to 55° C. The jacket of the reactor was heated until the reactormixture reaches 77+/−1° C. and then the preemulsion was fed into kettleover a period of 195 minutes. During the polymerization, the reactortemperature was maintained at 82.5+/−0.5° C. At the end of thepreemulsion delay charge, the reactor was held at 82° C. for 30 min. Thereactor contents were then cooled to 55° C., Trigonox and Parolite wereadded to the reactor, and the reactor contents held for 30 min. Afterthe post-cure period, the reactro contents were cooled to 35+/−1° C.,then Nofoam 1976 defoamer and Kathon LX biocide were added to thereactor.

The aqueous PSA polymers made according to the invention (Sample #1 andSample #2) appear to be white viscous emulsion containing no foreignmaterial such as insolubles, or coagulum. The total solid is from about56% to about 60 wt. %. Peel strength of the polymer products are shownbelow in Table 1.

The PSAs were formulated before testing. The following table is the PSAformulation recipe. Material Amount Mix time (min) GME-3210 100 AMP-950.7 30 Aerosol OT 1.0 45 Tacolyn 1070 30 60 Acusol 830 0.1˜0.4 60

TABLE 1 Peel Testing Results Sample #1 Sample #2 Facestock: INTEX INTEXCoatweight: 0.68″ GF 0.72″ GF SS PL (24 hr) 0.28a 0.18a 0.175a 0.14a GLPL (24 hr) 0.16a 0.12a 0.2a 0.1a SS PL (1wCTH) 0.25a 0.19a 0.3a 0.22a GLPL (1wCTH) 0.245a 0.12a 0.28a 0.17a SS PL (3d 70° C.) 0.05a 0.04a 0.05a0.025a GL PL (3d 70° C.) 0.04a 0.02a 0.02a 0.02a SS PL (1w 70° C.) 0.05a0.05a 0.05a 0.04a GL PL (1w 70° C.) 0.06a 0.05a 0.045a 0.03a SS PL (1wHum) 0.17a/g 1.05c 0.015a 0.01a GL PL (1w Hum) 0.18a/g 0.2aa/g 0.025a/g0.015a/gAbbreviations:SS: Stainless steel as substrate test plateGL: Glass as substrate test plateINTEX: PVC vinyl film INTEX Plastics CorporationGF: PVC vinyl film from General Formulations (GF)/VPI, Geon, Renolit,HPG)The results demonstrate that the crosslinked FSAs of the invention areremovable and plasticizer resistant (acceptable peel strength andadhesive, failure mode).

Example 2 Comparison

The polymers of Example 2 was polymerized according to the proceduredescribed in Example 1 except that 0.4 wt. % (2.4 g) of butenedioldiacrylate was used as crossliner. The polymerization procedure andamount of reactants were the same. Both crosslinkers were used in thesame mol amount as the ALMA, which is 0.026 mol in polymercoffespondingly (Diallylmnaleate: 5A48 g, Allylacrylamide 2.89 g).

Three formulations, BL2A, HL2B, and HL2C, are produced with differentlevels of tackifier (Tacolyn 1070). Peel strength of the polymerproducts are provided in Table 2. TABLE 2 Peel Strength - ButenediolDiacrylate Crosslinker PL PL PL Sample Tackifier substrate (20 min) (24hrs) (4 d@65° C.) HL2A 0   SS 1.25a 1.77a 1.72t 0   Glass 1.16a 1.22a1.5t HL2B 5% SS 1.72a 2.28a 1.7t 5% Glass 1.5a 1.89a 1.35a HL2C 15%  SS2.06a 2.67a 1.73 70% t 15%  Glass 1.65a 2.28a 1.35a

The results demonstrate that the crosslinked PSAs using butenedioldiacrylate as crosslinker are not removable (Peel Strength>0.3pound/inch).

Example 3 Comparison

The polymers of Example 3 were prepared according to the same procedureas described in Example 2, except 0.08 wt. % of hexenediol diacrylate(0.48 g) was used as the crosslinker. Four formulations (HL3A-D) weremade at different tackifier levels (Tacolyn 1070) from the same basepolymer, HL3U. Peel strength of the polymer products using the 180° C.dynamic peel testing is provided in Table 3. TABLE 3 Peel Strength -Hexenediol Diacrylate Crosslinker PL PL PL Sample Tackifier substrate(20 min) (24 hrs) (4 day @65° C.) HL3A 10% SS 3.85a 5.1a 5.8a 10% Glass4.37a 4.61a 6.13a HL3B 20% SS 3.98a 5.17a 5.91a 20% Glass 4.61a 5.02a6.36a HL3C 30% SS 4.24a 5.54a 6.22a 30% Glass 4.58a 4.47a 6.67a HL3D 40%SS 4.54a 4.91a 6.87a 40% Glass 5.04a 4.6a 6.12a

The results demonstrate that the crosslinked PSAs using hexenedioldiacrylate as crosslinker are not removable.

Example 4 Comparison

The polymers of Example 4 were polymerized according to the sameprocedures as disclosed in Example 3, except the amount of hexenedioldiacrylate crosslinker is 0.2 wt. % (HLAA) (1.2 g) and 0.4 wt. % (HLAB)(2.4 g), respectively. Both crosslinked PSAs using hexenediol diacrylateas crosslinker showed unacceptably high peel strengths with adhesivefailure mode similar to the results of the HL3 series in Example 3.

Example 5 Comparison

The polymers of Example 5 were polymerized according to the proceduredescribed in Example 1 except that allyl glycidyl ether (0.6 g AGE for0.1%, 1.4 g AGE for 0.25%, and 2.7 g AGE for 0.5%) was used ascrosslinker. Sample LT5A, LT5B and LT5C are samples with differentamount of crosslinker. The peel strength of the crosslinked PSA productsusing the 180° C. dynamic peel testing is provided in Table 4. TABLE 4Peel Strength of Polymers PL PL PL SAMPLE AGE % SUBSTRATE (20 hr) (24hr) (70° C./4 days) LT5A 0.1 SS 2.0c 3.2c 4.1t 0.1 Glass 1.5a/c 2.1a/c3.2t LT5B 0.25 SS 0.9a/t 2.4c/t 3.8c/t 0.25 Glass 0.8a/t 2.2c/t 3.0c/tLT5C 0.5 SS 0.7a/t 1.8c/t 3.4c/t 0.5 Glass 0.6a 1.2c/t 2.7c/t*Facestock: PVC film

Results demonstrate the crosslinked PSA using allyl glycidyl ether arenot removable with high peel strength and unacceptable failure mode.

Example 6

The polymers of Example 6 were polymerized according to the proceduredescribed in Example 1 except that the PSAs are crosslinked with ALMA(HL6A, invention), diallyl maleate (L6B, invention) and allyl acrylamide(HL6C, comparison). (2.89 g of crosslinker was used). ALMA crosslinkeris used at the level 0.0046 mol/100 g; wt. % is 0.059%. TABLE 5 PeelStrength of Polymers Peel test conditions PVC film INTEX PVC film GFSubstrate sample HL6A HL6B HL6C HL6A HL6B HL6C coatweight 0.72 0.67 0.650.72 0.67 0.65 SS PL (24 hr) 0.06a 0.13a 1.8a 0.05a 0.025a 1.81a GL0.06a 0.06a 1.62a 0.05a 0.05a 0.58a SS PL (1 week CTH) 0.12a 0.2a 1.58a0.18a 0.19a 1.79a GL 0.145a 0.14a 1.75a 0.13a 0.07a 1.39a SS PL (1 week70° C.) 0.08 15% t 0.03a/g 0.16t 0.09a 0.02a/g 0.085a/g 0.08a GL 0.0815% t 0.02a/g 0.135a/g 0.06a 0.025a/g 0.09a/g 0.06a 40% t

The experimental results demonstrate that crosslinked PSA polymersprepared using diallyl maleate and allyl methacrylate as crosslinkersare removable from test plate (substrate). PSA samples prepared usingallyl acrylamide as crosslinker show unacceptably high peel strengthand/or unacceptable adhesive failure mode.

1. A removable, plasticizer resistant pressure sensitive adhesivecomprising a crosslinked aqueous emulsion polymer comprising: (a) atleast one hydrophobic monomer selected from an alkyl (meth)acrylateester of an alcohol wherein the alkyl portion of the alcohol is linearor branched and contains at least 4 carbon atoms; (b) about 0.2 to about10 wt. % of at least one hydrophilic monomer; and (c) about 1 to about40 wt. % of one partially hydrophilic monomer selected from alkyl(meth)acrylate esters of an alcohol wherein the alkyl portion of thealcohol has 1 to 2 carbon atoms, N-vinyl-2-pyrrolidone, or mixturesthereof; and (d) an effective amount of a crosslinker selected fromdiallyl maleate or compounds represented by the formula:

wherein R is selected from hydrogen, methyl, or ethyl, and R′ isselected from vinyl (—HC═CH₂), allyl (—CH₂—CH═CH₂), or methallyl(—C(—CH₂)═CH₂); wherein said pressure sensitive adhesive does notcontain a plasticizer.
 2. The composition of claim 1 wherein saidremovable, plasticizer resistant pressure sensitive adhesive has aninitial peel strength of less than about 0.3 pounds per inch peel forcewith adhesive failure mode.
 3. The composition of claim 1 wherein theamount of monomer (a) in said crosslinked aqueous emulsion polymer isabout 50 to about 90 wt. %.
 4. The composition of claim 1 wherein theamount of monomer (a) in said crosslinked aqueous emulsion polymer isabout 60 to about 84 wt. %.
 5. The composition of claim 4 wherein theamount of monomer (a) in said crosslinked aqueous emulsion polymer isabout 70 to about 80 wt. %.
 6. The composition of claim 1 wherein theamount of monomer (b) in said crosslinked aqueous emulsion polymer isabout 0.2 to about 5 wt. %.
 7. The composition of claim 6 wherein theamount of monomer (b) in said crosslinked aqueous emulsion polymer isabout 1 to about 3 wt. %.
 8. The composition of claim 1 wherein theamount of monomer (c) in said crosslinked aqueous emulsion polymer isabout 10 to about 25 wt. %.
 9. The composition of claim 8 wherein theamount of monomer (c) in said crosslinked aqueous emulsion polymer isabout 12 to about 25 wt. %.
 10. The composition of claim 1 wherein saidmonomer (a) is selected from isooctyl acrylate, 4-methyl-2-pentylacrylate, 2-methylbutyl acrylate, isoamyl acrylate, sec-butyl acrylate,n-butyl acrylate, 2-ethylhexyl acrylate, isodecyl methacrylate, isononylacrylate, isodecyl acrylate, or mixtures thereof.
 11. The composition ofclaim 10 wherein said monomer (a) is 2-ethyl-hexyl acrylate, n-butylacrylate, and mixtures thereof.
 12. The composition of claim 1 whereinsaid monomer (b) is selected from a monoolefinic monocarboxylic acid, amonoolefinic dicarboxylic acid, 2-hydroxyethyl acrylate, or mixturesthereof.
 13. The composition of claim 12 wherein said monomer (b) isselected from acrylic acid, methacrylic acid, fumaric acid, maleic acid,itaconic acid, crotonic acid, oligomeric acrylic acid, 2-hydroxyethylacrylate, or mixtures thereof.
 14. The composition of claim 13 whereinsaid monomer (b) is acrylic acid, 2-hydroxyethyl acrylate, methacrylicacid, or mixtures thereof.
 15. The composition of claim 1 wherein saidmonomer (c) is selected from methyl acrylate, methyl methacrylate, ethylacrylate, N-vinyl-2-pyrrolidone or mixtures thereof.
 16. The compositionof claim 15 wherein said monomer (c) is ethyl acrylate.
 17. Thecomposition of claim 1 wherein the amount of said crosslinker is fromabout 0.2 to about 1.0 wt. %.
 18. The composition of claim 17 whereinthe amount of said crosslinker is from about 0.3 to about 0.6 wt. %. 19.The composition of claim 17 wherein said crosslinker is represented bythe formula:

wherein R is selected from hydrogen, methyl, or ethyl, and R′ isselected from vinyl (—HC═CH₂), allyl (—CH₂—CH═CH₂), or methallyl(—C(—CH₂)═CH₂).
 20. The composition of claim 19 wherein said crosslinkeris selected from allyl acrylate, allyl methacrylate, vinyl acrylate,vinyl methacrylate, methallyl acrylate, methallyl methacrylate, ormixtures thereof.
 21. The composition of claim 20 wherein saidcrosslinker is allyl acrylate or allyl methacrylate.
 22. The compositionof claim 17 wherein said crosslinker is diallyl maleate.
 23. Aremovable, plasticizer resistant pressure sensitive adhesive comprisinga crosslinked aqueous emulsion polymer comprising: (a) from about 70 toabout 80 wt. % amount of 2-ethylhexyl acrylate, n-butyl acrylate, ormixtures thereof; (b) from about 1 to about 3 wt. % of acrylic acid,2-hydroxyethyl acrylate, methacrylic acid, or mixtures thereof; (c) fromabout 12 to about 25 wt. % of ethyl acrylate; and (d) from about 0.3% toabout 0.6 wt. % of diallyl maleate, allyl methacrylate, allyl acrylateor mixtures thereof; wherein said pressure sensitive adhesive does notcontain a plasticizer 24-26. (canceled)